Sequential statistical mechanics/quantum

The previous discussion pointed out some well-known limitations of the different theoretical approaches currently used to analyse polarization effects and estimate the dipole moment in the liquid phase. We will focus the present analysis of polarization effects in HB liquids on results obtained by using the sequential statistical mechanics/quantum mechanics approach. 

The analysis of the properties of mesityl oxide in aqueous solution was based on the continuous and discrete models of the solvent. Here, we used the polarizable continuum model (PCM) [32, 33], and for the discrete model of the solvent, we performed the sequential use of quantum mechanics and molecular mechanics methods, S-QM/MM [20, 21]. In the S-QM/MM procedure, initially the liquid-phase configurations are sampled from molecular simulations, and after statistical analysis, only configurations with less than 10 % of statistical correlation are selected and submitted to quantum mechanical calculations. In our study, we used the Monte Carlo method (MC) with... 

Theoretical chemistry is informed by the observation of charge density distributions in crystals and molecules, and these do not appear as sets of discrete points. Conventional wisdom implicates the time scale of diffraction experiments for building up, what appears to be diffuse charge densities, by the statistical accumulation of data points. However, not only does quantum theory deny the existence of electronic positions and paths, but until it has been shown experimentally that the data points appear sequentially, the statistical argument is no more persuasive than the wave-mechanical. 

An approach based on the sequential use of Monte Carlo simulation and Quantum Mechanics is suggested for the treatment of solvent effects with special attention to solvatochromic shifts. The basic idea is to treat the solute, the solvent and its interaction by quantum mechanics. This is a totally discrete model that avoids the use of a dielectric continuum. Statistical analysis is used to obtain uncorrelated structures. The radial distribution function is used to determine the solvation shells. Quantum mechanical calculations are then performed in supermolecular structures and the spectral shifts are obtained using ensemble average. Attention is also given to the case of specific hydrogen bond between the solute and solvent. 

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